A total of 341 stool specimens known to be positive for group A rotaviruses by RNA electrophoresis had been obtained from various locations in Malaysia from children below the age of five years who had gastroenteritis. These stool specimens which were collected from 7 of the 12 years spanning 1977-1988 were brought to the NIH for determination of the serotypes circulating in Malaysia and for further characterization by molecular biologic techniques. Ten percent suspensions of 294 specimens were tested for antigen by a pre-post confirmatory ELISA. Forty-seven specimens appeared to be too dilute or were limited in quantity and thus, were not tested by this system, but rather were passaged into primary African green monkey kidney (AGMK) cells using the method of Ward et al. (1984). Of the 285 specimens that were ELISA positive, 176 could be serotyped: 71% belonged to serotype 4, 15% to serotype 1, 4% to serotype 3 and 3% to serotype 2. In addition, 6% displayed ambiguous serotype specificities, reacting to more than one monoclonal antibody, and need to be investigated further.